Conversion of oxygenated hydrocarbon, such as methanol, to olefins and other unsaturated compounds is a commonly used reaction scheme for chemical manufacture. Conventional methods can involve exposing an oxygenated hydrocarbon feed to a molecular sieve, such as ZSM-5. In addition to forming olefins, some desirable aromatic compounds can also be formed, such as para-xylene.
U.S. Pat. Nos. 4,049,573 and 4,088,706 disclose conversion of methanol to a hydrocarbon mixture rich in C2-C3 olefins and mononuclear aromatics, particularly p-xylene, by contacting the methanol at a temperature of 250-700° C. and a pressure of 0.2 to 30 atmospheres with a crystalline aluminosilicate zeolite catalyst which has a Constraint Index of 1-12 and which has been modified by the addition of an oxide of boron or magnesium either alone or in combination or in further combination with oxide of phosphorus. The above-identified disclosures are incorporated herein by reference.
Methanol can be converted to gasoline employing the methanol to gasoline (“MTG”) process. The MTG process is disclosed in the patent art, including, for example, U.S. Pat. Nos. 3,894,103; 3,894,104; 3,894,107; 4,035,430 and 4,058,576. U.S. Pat. No. 3,894,102 discloses the conversion of synthesis gas to gasoline. MTG processes provide a simple means of converting syngas to high-quality gasoline. The ZSM-5 catalyst used is highly selective to gasoline under methanol conversion conditions, and is not known to produce distillate range fuels, because the C10+ olefin precursors of the desired distillate are rapidly converted via hydrogen transfer to heavy polymethylaromatics and C4 to C8 isoparaffins under methanol conversion conditions. The above-identified disclosures are incorporated herein by reference.
Chinese publications CN 101602648, CN 101602643, CN 101607864, and CN 101780417 describe use of selectivated catalysts for conversion of methanol to para-xylene. In these publications, zeolite catalysts are treated with silicate compounds, such as tetraethylorthosilicate, to provide improved selectivity for formation of olefins and para-xylene from methanol feeds. However, silicon treatment introduces several undesired effects, it reduces the per pass aromatic yield and promotes coke deposition that limits the catalyst cycle length. Especially for metal promoted zeolites, silicon treatment can promote metal migration and sintering that results in shorter catalyst lifetime.
The methanol to paraxylene and olefins process (“M2PXO”) is a new technology that produces olefins and aromatics at high yields from oxygenated hydrocarbon feeds such as methanol. Provisional U.S. Patent Publication No. 2015/0175498, incorporated here in entirety by reference, describes processes utilizing a catalyst comprising at least one molecular sieve and at least one element selected from Groups 2-12 of the Periodic Table of the Elements. U.S. Patent Publication No. 2015/0175499, incorporated here by reference in its entirety, describes improved aromatics and olefins yield by preparation of molecular sieve (zeolite) catalysts combined with effective conversion conditions. Preparations include modification of the catalyst with a transition metal, steaming of the catalyst, and/or modification of the catalyst with phosphorous.
Despite these advances, the M2PXO process consists of multiple reactions having competitive kinetics including undesired reactions such as methanol decomposition to water and carbon monoxide, alkylation of aromatics with methanol to create undesired aromatics have 9 or more carbon atoms, and other undesired reactions producing coke, methane, carbon monoxide, and carbon dioxide. These competitive kinetics and undesired reactions present a barrier to further maximizing the aromatics selectivity when produced from oxygenated hydrocarbon feeds. There is an ongoing need to provide improved methods for producing aromatics from oxygenated feeds.